Current collector for rotating machines



May 28, 1946. E. KOBEL 2,401,166

CURRENT COLLECTOR FOR ROTATING MACHINES Filed Aug. 4, 1945 3 Fa. a 7 4 Patented May 28, 1946 CURRENT COLLECTOR FOR ROTATING MACHINES Ernst Kobel, Ennetbaden, Switzerland, assignor to Aktiengesellschaft Brown, Boverie & Cie.,

Baden, Switzerland Application August 4, 1943, Serial No. 497,379 In Switzerland May 16, 1942 4 Claims.

The known current collectors for unipolar machines where mercury is used as the contact metal between a rotating and a stationary metal body possess the undesirable property that the transition resistance between the solid metal and the mercury is relatively high. The voltage drop at the current collectors is thus correspondingly large and irregular and the losses at these points are also considerable.

Tests have now shown that this is due to the imperfect wetting of the iron rings by the mercury, iron being the only non-amalgamatlng metal which can be employed, and furthermore it has been found that the wetting by the mercury is much improved and the voltage drop smaller and more uniform if in accordance with the invention the contact points are at least temporarily maintained at such a high temperature that the adhesion forces between the mercury and the solid metal exceed the cohesion of the 11181.- cury, At the same time special means must be provided to prevent mercury vapour from passing into the machine space.

The necessary temperature which exceeds 100 C. and may amount to several hundred degrees forms during the wetting process. It is therefore not necessary to maintain the temperature at a high value during the whole time the machine is in operation, one to two hours per day often being sufficient.

Two constructional examples of the invention are illustrated in the drawing, the right half of a unipolar machine being shown in longitudinal section in each figure. In Fig. 1 the rotating part of the current collector lies outside the stationary part, whilst in Fig. 2 the arrangement is reversed.

In both figures the stationary magnet frame is indicated by the reference numeral I, 2 is the rotating armature and 3 the excitation winding. The bearings l for the armature 2 are located outside the magnet frame I; In Fig. 1 the thicker middle piece of the armature 2 forms a hollow channel 5 into which the stationary current collecting ring 6 penetrates. When the armature 2 rotates the gap between both is filled with mercury I, the outer layer of which is carried along by the inner surface of the hollow channel 5 and can either be attained by special heating devices or very advantageously by the natural friction between the mercury and the iron when the current transition points are insulated against heat losses. By this means the unavoidable frictional losses are employed to reduce the electrical losses at the current collecting points.

The mercury vapours which occur must be collected and in order to condense, cooled at another point where no loss of frictional heat would thus occur, for instance shortly before the passage leading from the interior of the machine to the outside. The condensed mercury is then returned to the contact points and this can be achieved either by natural or forced circulation. The machine is preferably so constructed that its excitation windings do not come into contact with the mercury vapour, these being located beyond the range of the mercury circuit. The excitation windings should also be arranged to be outside of the heat insulation of the contact points so that the cooling of the windings is not affected.

In order to prevent the oxidization of the liquid metal or its vapour it is expedient to collect the current in an atmosphere which is practically free from oxygen.

Tests have shown that the transition resistance remains small for a long time even when the temperature is lowered again. This phenomenon is due to the increase in the adhesion surface which pressed against the rotating contact surface by centrifugal force. Current collecting ring 6 is supported by the electrically conductive flange 8 which is fixed to the magnet frame I, there being an intermediate layer of insulating material 9 between the latter and the flange 8. One terminal I 0 of the machine is connected to the flange 8 and passes through an insulating bushing in the frame I. Both sides of flange 8 are well covered with heat insulating material II and also the current collecting ring 6 is heat insulated at l2 on the armature side.

In the hollow space [3 which contains the excitation coil 3 there is a cooling ring I4 through which cooling water, which enters at l5 and emerges at 5, circulates. This cooling ring encloses with its hollow conical surface the conical ring ll; in the narrow conical gap I8 thus formed the mercury vapour which is given off from the heated current collector mercury I is condensed to liquid mercury. Thi liquid mercury is splashed from the edge IQ of the ring I! into a groove 20 where it collects and is drawn off by the pump 2| through the suction pipe 22 and passed through pipe 23 back to the mercury l in the hollow groove 5. 1

With the embodiment shown in Fig. 2 a conical mercury condensing slot I 8 is also provided which is located between the rotating conical ring I! and a stationary cooling ring l4 having a conical bore. In this case the edge IQ of the conical ring IT projects into the current collecting groove 24.

This latter is formed by the outer rings 28, 2| fixed in the frame I and the projecting annular collar 21 on the rotating armature! andisfilled with mercury I due to centrifugal force. Not only are the end surfaces of the double ring 25, 20 forming the groove 24 provided with a good heat insulation but the groove is also heated. For this Dul'D0 e electrical heating elements 29 are embedded in the heating insulation 28. Since there is agap between the insulation 28 and the coolingring I this must be bridged over for the mercury which fiows back from the cooling gap ll to the groove 24; for this purpose a metal tunnel 30 is provided. Those elements in Fig. 2 which are not specially mentioned here have the same reference numerals as the corresponding elements in Fig. 1.

I claim:

1. In a dynamo electric machine, a current collector comprising a rotor ring and a stator ring positioned to define a gap therebetween, a body of mercury in said gap to provide electrical contact between the rotor and the stator ring, and cooling means for condensing mercury vapor arising from said :body oi mercury due to frictional heat, said cooling means being spaced substantially from said body of mercury whereby to maintain said body of mercury at a high temperature.

2. In a dynamo electric machine, a current collector as defined in claim 1 wherein heat insulating means is positioned between said body of mercury and said cooling means.

3. In a dynamo electric machine, a current collector as defined in claim 1 including means for supplying additional heat to said body of mercury.

4. In a dynamo electric machine, a current 1- lector as defined in claim 1 including means roviding a conduit for the return of condensed ercury from said cooling means to said bod oi go mercury.

ERNST KOBEL. 

